About 40 percent of Americans over 40 complain of dizziness at some time. In many cases, loss or damage of sensory cells in the inner ear is implicated. Dysequilibrium negatively impacts quality of life and productivity and can lead to depression and anxiety. Much remains unknown about the normal function of sensory cells in mammalian vestibular organs, which provide the input to reflexes that maintain balance and gaze. I propose to study stimulus processing by sensory cells in the mouse utricle. Hair cells, the sensory receptors of the inner ear, contain voltage and mechanically gated conductances that interact to shape the signals sent to the central nervous system. The mouse utricle contains two types of hair cells distributed throughout the organ. These cells are contacted by three types of vestibular afferents whose discharge properties vary systematically with the region of the utricle they innervate. The mechanisms underlying this regional organization are unknown, but are likely to include regional differences in the voltage and mechanically gated channels of hair cells. How the expression, voltage ranges of activation, or adaptation kinetics of these conductances vary is not known. Preliminary data show variations among utricular hair cells in ion channel expression, voltage ranges of activation and adaptation kinetics, but whether these or other differences are regionally organized is not known. This proposal aims to investigate whether hair cell properties vary with region and whether the differences observed explain differences in afferent firing properties.